Tubular structures such as pipe are typically manufactured in straight lengths. Individual lengths or joints of pipe may be connected together to form a conduit or a pipeline.
It is frequently necessary to bend pipe in order to provide a bend in a pipeline. Pipe may be bent in a shop using a stationary bending apparatus, or may be bent in a yard or in the field using a mobile bending apparatus.
In either case, the pipe is typically bent by applying one or more forces to the pipe in order to bend the pipe around a pipe bending shoe which is positioned adjacent the pipe.
As one non-limiting example of a pipe bending procedure, a pipe may be supported by supports located at both ends of the pipe, a pipe bending shoe may be located between the ends of the pipe, and forces may be applied to one or more of the supports and/or the pipe bending shoe in order to cause the pipe to bend around the pipe bending shoe.
As a second non-limiting example of a pipe bending procedure, a pipe may be supported by a cantilever support located at a first end of the pipe, a pipe bending shoe may be located between the cantilever support and a second end of the pipe, and a force may be applied to the second end of the pipe in order to cause the pipe to bend around the pipe bending shoe.
As a third non-limiting example of a pipe bending procedure, a first end of a pipe may be supported by a ground surface, a pipe bending shoe may be located between the first end and a second end of the pipe, and an upward force may be applied to the second end of the pipe in order to cause the pipe to bend around the pipe bending shoe. This third exemplary pipe bending procedure is often performed in the field using a tractor having a pipe bending shoe mounted thereon, wherein the upward force is provided by a winch on the tractor.
A challenge in bending pipe is to avoid collapse of the pipe wall as a portion of the circumference of the pipe is placed in compression and a portion of the circumference of the pipe is placed in tension during the pipe bending procedure. The tendency of a pipe wall to flatten during bending increases as the diameter of the pipe increases. In addition, pipe which is coated with a layer of a protective or insulating material is particularly susceptible to damage to the coating during a pipe bending procedure, either due to the force which is applied directly to the coating by the pipe bending shoe or due to the deformation of the underlying pipe during the pipe bending procedure.
A number of different styles of pipe bending shoe are known.
A first exemplary style of pipe bending shoe includes a rigid die which defines a pipe channel having a convex longitudinal profile. At the initiation of a pipe bending procedure, a relatively small area of the pipe channel is in contact with the pipe. As the pipe bending procedure continues and the amount of force which is applied to the pipe increases, the amount of area of the pipe channel which is in contact with the pipe progressively increases as the pipe is bent to conform with the convex longitudinal profile of the pipe channel. An advantage of this first style of pipe bending shoe is that the contact area between the pipe bending shoe and the pipe increases as increasing force is applied to the pipe in order to bend the pipe around the pipe bending shoe. A disadvantage of this first style of pipe bending shoe is that the rigidity of the pipe channel may increase the risk of damage to a coating which has been applied to the pipe. An example of this first style of pipe bending shoe are the Proline™ Pipe Bending Die Sets which are manufactured by Proline Pipe Equipment Inc. of Edmonton, Alberta, Canada.
A second exemplary style of pipe bending shoe includes a frame upon which are mounted a plurality of discrete spring-loaded segments which are arranged end to end to define a pipe channel. At rest, the spring-loaded segments have a straight longitudinal profile. As a pipe is bent around the pipe bending shoe, the spring-loaded segments deflect to conform with the developing bend in the pipe. An advantage of this second style of pipe bending shoe is that each of the spring-loaded segments may be in contact with the pipe during the entire pipe bending procedure. A disadvantage of this second style of pipe bending shoe is that the force which is applied to the pipe by the pipe bending shoe during the pipe bending procedure may not be evenly distributed amongst the spring-loaded segments, which may increase the risk of collapse of the pipe wall and/or damage to a coating which has been applied to the pipe. An example of this second style of pipe bending shoe is the Proline™ Tractor Bending Shoe which is manufactured by Praline Pipe Equipment Inc. of Edmonton, Alberta, Canada.
A third exemplary style of pipe bending shoe is described in U.S. Pat. No. 5,123,272 (Heaman). This pipe bending shoe includes a pressure member having a material contacting surface divided into a plurality of discrete transverse segments which are movable during the bending process to accommodate a bend in the material, and includes means for distributing the load among the segments so that the load required for the proper bending moment is distributed among all of the segments. A disadvantage of this third style of pipe bending shoe is that the means for distributing the load among the segments may be relatively complex.
A fourth exemplary style of pipe bending shoe is described in U.S. Pat. No. 5,600,993 (Heaman). This pipe bending shoe includes a pair of straight resilient spring-like shafts, a single flexible web extending between the pair of shafts, and means for securing the flexible web to the resilient shafts. The pipe bending shoe may further include a plurality of flexible tubular rollers extending over the shafts. During a pipe bending procedure, the resilient shafts and the flexible rollers flex to accommodate the bending of the pipe so that the flexible web maintains contact with the pipe. The resilient shafts and the flexible rollers spring back to their original straight configuration when the pipe bending procedure is completed. One advantage of this fourth style of pipe bending shoe is that the flexible web appears to maintain contact with the pipe during the entire pipe bending procedure. Another advantage of this fourth style of pipe bending shoe is that the flexible web provides a flexible engagement surface for the pipe which may reduce the risk of damage to a coating which has been applied to the pipe. A disadvantage of this fourth style of pipe bending shoe is that the force which is applied to the pipe by the pipe bending shoe during the pipe bending procedure may not be evenly distributed along the entire length of the flexible web.
A fifth exemplary style of pipe bending shoe is described in U.S. Pat. No. 7,047,789 (Theener). This pipe bending shoe includes a pin up plate, a first framework pivotally attached to the pin up plate, a second framework pivotally attached to the pin up plate, and a plurality of discrete belts having a first end attached to the first framework and having a second end attached to the second framework, wherein the belts are disposed to an outer surface of a pipe wall in a region which becomes a minor radius of a bend in the pipe. The plurality of belts provide a transversely segmented pipe sling which maintains a straight longitudinal profile during bending of a pipe. An advantage of this fifth style of pipe bending shoe is that the plurality of belts provide a flexible engagement surface for the pipe, which may reduce the risk of damage to a coating which has been applied to the pipe. A disadvantage of this fifth style of pipe bending shoe is that the force which is applied to the pipe by the pipe bending shoe during the pipe bending procedure may not be evenly distributed amongst the belts, which may increase the risk of collapse of the pipe wall and/or damage to a coating which has been applied to the pipe.